Can there be a difference in a ct and pet scan of 1mm in the results of a lung nodule?

Yes: A 1 mm difference in the size of a lesion imaged by two different scans (or even in 2 sequential scans done by the same machine) is usually of no significance. You have to put it all in the context of clinical condition, presence of other lesions, and change over time.

Yes and no: The difference may not be real because the lung and the nodule are three-dimensional structures and ct and pet are two-dimensional and it depends which way the sections are made, which is never the same depending on how you are positioned in the scanner.

Absolutely: Ct scans and pet scans cut the body into slices of variable thickness (usually 2-5 mm), so it is definitely possible to cut through a different portion of the nodule on two scans - even if performed on the same day.

Yes: There are differences in techniques between the ct scan with a pet scan and a general ct scan. Additionally, radiologists may measure a nodule slightly differently. Please look at a ruler and realize just how small 1 mm is. Radiologists routinely are measuring things less than 1 cm or about 3/8 of an inch.